An interference pattern caused by the reflection of light between two surfaces, a spherical and an adjacent flat surface is known as Newton’s Rings. These patterns are formed by light incident on the thin film of air between the convex surface of a convex lens and a flat glass plate. These patterns are circular in shape because the air film formed is wedge shaped. Sir Isaac Newton studied the effect in 1717.
Theory: – These rings are fringes of equal thickness. These fringes can be observed when light is reflected from a Plano- convex lens with a long focal length that is placed with an adjacent flat lens. A thin air film is formed between both the lenses. Thickness of this air film varies from zero to some value t.
When the lens setup is illuminated with monochromatic light falling on it, then concentric dark and bright interference rings can be observed in the reflected light. These circular fringes are known as Newton’s rings.
Questions & Answers: –
- Why is the flat glass plate is inclined at an angle of 45°?
This inclined glass plate turns the light rays coming from an extended source to 90° and light falls normally on the convex surface.
- Why do these rings have a dark center?
The path difference is zero at the point of contact but one of the light rays is reflected the condition of minimum intensity is created leaving a dark spot at the center.
- What will happen if we replace the sodium light with white light in the experiment?
A few colored fringes will be observed near the center.